This invention relates to the cleaning of a semiconductor processing chamber. More particularly, the present invention relates to in-situ cleaning of a semiconductor deposition chamber using anhydrous hydrogen fluoride (HF).
Semiconductor processing chambers such as deposition reactors are widely used in the semiconductor industry to deposit films of material onto substrates. Deposition reactors may include reactors such as plasma-enhanced chemical-vapor deposition (PECVD), physical vapor deposition (PVD), or chemical vapor deposition (CVD) reactors, all of which are well known to those skilled in the art.
When a deposition reactor is employed for depositing material on a substrate, e.g., on a semiconductor wafer or a glass panel for fabrication of flat panel displays, the deposition material may undesirably collect on the inside surfaces of the deposition chamber, e.g., chamber sidewalls or substrate holder, etc. Periodically, this unwanted deposition material must be removed from the chamber inner surfaces before the accumulated build-up interferes with deposition process performance, e.g., by contaminating the substrate in subsequent depositions. Glass materials, such as silicon dioxide (SiO.sub.2) and borophosphosilicate glass (BPSG), are common examples of deposition materials that may be undesirably accumulated inside the deposition chamber and may interfere with subsequent depositions.
Undesirable accumulation of glass material, e.g., silicon dioxide (SiO.sub.2), may take place, for example, during fabrication of a metal oxide semiconductor (MOS) transistor. As is well known to those skilled, silicon dioxide (SiO.sub.2) is typically employed as the dielectric insulating material, and multiple layers of silicon dioxide (SiO.sub.2) may be deposited on a substrate before the fabrication of the desired circuit is completed. Glass deposition may also take place, as is well known, during the fabrication of devices other than MOS transistors.
With reference to silicon dioxide (SiO2), for example, this material may be deposited using any of the conventional deposition chambers. For consistency of illustration, the remaining disclosure is discussed in connection with a thermal chemical vapor deposition system, particularly one known as the DSM9800.TM. CVD system, which is available from Lam Research Corporation of Fremont, Calif. It should be borne in mind, however, that the inventive in-situ cleaning process may apply to any semiconductor processing chamber, whether or not involving plasma, in which removal of unwanted deposition material, e.g., glass deposition, is desired.
FIG. 1 illustrates a simplified schematic of a deposition chamber representing, for example, a reactor chamber of the aforementioned DSM9800.RTM. CVD system. As shown in FIG. 1, a deposition chamber 20 may include a gas inlet 52 for introducing a deposition source gas, e.g., silane, triethylorthosilicate (TEOS), diborosilane and others familiar to those skilled in the art, into the interior of deposition chamber 20. The deposition source gas, when exposed to a deposition temperature ranging from between about 700.degree. C. to about 900.degree. C., may at least partially decompose to facilitate the deposition of some decomposed gas component(s) on a substrate 50, e.g., a silicon wafer, which may be secured on a work piece holder or chuck 54. The remaining unused deposition gas and byproduct gases, which may include volatile and residual gases, may be exhausted through an outlet port 56. An energy source 66 representing for example a series of lamps provide regular infrared heating, a graphite heater, or any other suitable energy source may be employed to maintain a suitable temperature within the deposition chamber to facilitate deposition.
In a number of cases, the insides of the deposition chamber 20, e.g., reactor side-walls 58, 60, 62, 64 and chuck 54, may also be at the appropriate temperature to induce deposition. Accordingly, these surfaces may be undesirably coated with the deposited materials which, as discussed hereinabove, may build up over time and potentially interfere with deposition process performance.
The above discussion applies primarily to thermal CVD reactors, i.e., reactors in which deposition occurs via a heat activated reaction. In plasma-enhanced deposition chambers, e.g., those employing an ECR (electron cyclotron resonance) power source, parallel plates, or TCP.TM. coils (whether or not planar) to inductively or capacitively couple the plasma, a plasma may be struck within the deposition chamber with the deposition source gas to facilitate deposition on a substrate. The mechanisms associated with plasma-enhanced deposition, as well as physical vapor deposition, are well known to those skilled in the art and are not repeated here in order not to unnecessarily obscure the invention.
Although plasma-enhanced deposition may, in some cases, more effectively control the directionality of the deposition material, it is found that some of the surfaces within the plasma deposition chamber may also be coated with the deposition material after a number of deposition operations. This is particularly true for surfaces directly exposed to the plasma.
The unwanted SiO.sub.2 deposition may be removed either by an in-situ process or by taking the reactor apart and manually clean the components. In-situ cleaning is generally desirable since it does not require disassembly of the reactor chamber and does not involve the concomitant down time associated therewith. In the prior art, in-situ cleaning may be achieved by sputtering the accumulated layers with plasma created from an inert gas, such as argon or nitrogen. The sputtering operation typically involves introducing inert gas into the deposition chamber and striking a plasma with the introduced inert gas to accelerate the ions toward the desired target surfaces, e.g., surfaces where there are unwanted SiO.sub.2 depositions. The sputtered material is then removed from the deposition chamber by evacuating it via an outlet port.
The above described sputtering technique, however, suffers from a major drawback. The SiO.sub.2 deposition film on the interior surfaces may not be uniform throughout, i.e., there may exist uneven depositions of SiO.sub.2 on the chamber's side-walls. During sputtering of SiO.sub.2, some of the soft side-wall material (comprising aluminum in some systems) in areas no longer covered by accumulated SiO.sub.2 may also be sputtered off. As a result, the deposition chamber side-wall may be thinned slightly with each cleaning cycle and may eventually fail over time.
Another method that is typically employed to clean accumulated SiO.sub.2 involves using a plasma formed from nitrogen trifluoride (NF.sub.3). In the presence of plasma, NF.sub.3 decomposes to produce free fluorine ions, which react with the silicon (Si) species in SiO.sub.2 to produce silicon tetrafluoride (SiF.sub.4) gas and oxygen (O.sub.2) gas. The reaction byproducts are then pumped out of the deposition chamber as waste.
Although the NF.sub.3 plasma cleaning technique is less physically damaging to interior walls of the deposition chamber (relative to the sputtering cleaning technique), this method has several drawbacks. NF.sub.3 source gas is expensive to purchase, toxic to handle, and relatively inefficient in cleaning, e.g., typically achieving an SiO.sub.2 etch rate of only about 4,000 angstroms/min to about 8,000 angstroms/min. NF.sub.3 residues, some of which may be exhausted out of the chamber, is also dangerous and expensive to dispose of. Further, the NF.sub.3 plasma cleaning technique produces flourine ions, which sputters the aluminum to form silicon tetrafluoride (SiF.sub.4) nodules as a byproduct. As can be appreciated by those skilled, the undesirable formation of aluminum tetrafluoride (AlF.sub.4) nodules via flourine ion sputtering may lead to further contamination of subsequent depositions.
Further, both of the above approaches require plasma to perform their cleaning functions. Accordingly, they are not well suited to cleaning reactors which do not employ or have the ability to generate plasma, e.g., thermally activated deposition chambers. In view of the foregoing, what is needed is an improved method of in-situ cleaning reactor chambers.